Volume at weekly venues

MARK HENRY 2024-08-22

How shall we set the volume level at weekly dancing events to avoid damaging dancers' hearing?

Rather than make recommendations to venue organizers, this document takes an educational angle, grounding the community conversation in the tradeoffs.

Volume

Peak level can damage your hearing if it is high—think of an explosion that leaves your ears ringing—but for our purposes we are focused on average, not peak, level.

Too loud

Survey of standards

• The World Health Organization (WHO) global standard for safe listening venues and events [1] specifies an upper limit of 100 L_{Aeq 15min} of music at a measurement position in the center of the dancefloor, at head height, with a clear line of sight to the speakers.

  The WHO chose this limit based on the WHO's previous noise guidelines [2] and assuming patrons that attend the venue for two hours once per month (see [1], Annex 2). Using the equal energy principle we can show that WHO's reference exposure of 80 dBA x 40 hrs/week is equal to 92 dBA x 3 hours/week. So, besides recommending an upper limit of 100 L_{Aeq 15m}, this standard implies a recommended exposure limit of 92 L_{A, 3h/wk}.

• NIOSH [6] specifies a limit of 85 dBA of noise for an 8-hour workday.

• According to a review conducted by the American Audio Engineering Society, European guidelines for adult audiences have limits ranging from 99 to 107 dBA at a variety of integration times. ([5], pg 14)

What these standards recommend for you

Doing the math, we can show that these exposures are equivalent to the following limits:

Calculation method: For the WHO standard, we used the equal energy principle with an exchange rate of 3 dB = halved time, calculated from 100 dBA for 2 hours/month. For NIOSH, we calculated from 85 dBA for 40 hours/week.

Damage

The following table was derived from the ISO 1999 standard [3], which is the most widely accepted model for predicting the probability of PTS for a given sound dose. LEX is the equivalent 8-hour workday noise level, which is what ISO 1999 uses. All NIPTS values are for 4kHz because that's where the most loss tends to occur, and all values are median, 50th percentile values—some individuals may experience more or less hearing loss depending on their susceptibility.

Interpretive notes:

1. At the WHO standard exposure level (92 dBA for 3h/week), the NIPTS after 40 years (2.15 dB) is relatively small compared to the expected ARHL (11.8 dB).
2. Exceeding the guideline by 3 dB more than doubles the NIPTS after 40 years (4.98 dB). While this is still less than the expected ARHL, it represents a notable increase in hearing loss risk for the median exposed individual.
3. Exceeding the guideline by 6 dB results in a 40-year NIPTS (8.98 dB) that, while not exceeding the expected ARHL, becomes a significant contributor to overall hearing loss when combined with ARHL for the average exposed person.

Measurement and metering

Note: as you move closer to the speaker, the dBA will go up; as you move away from it, the dBA will go down. A volume policy should specify where to make a measurement from.

I'll now discuss phone apps and cheap db meters. Pro-grade calibrated measurement is still too expensive for us. What can we do instead?

Apps

For iOS, the NIOSH Sound Level Meter App is the best available.

Note that because Android hardware is not standardized, Android apps are necessarily less calibrated out of the box. However, I can recommend SmarterNoise for Android users, which can show a L_{Aeq 1min} readout.

Regardless of what app you use, calibrate it by comparing it to a meter or an app on someone else's phone. Any adjustment will provide better calibration for our purposes.

Cheap meter

Get a cheap meter from Amazon. Set it to A-weighted db and set it to "slow mode". Really we would like a 15-min average, which is slower than "slow mode," but you can eyeball it.

Venue design and miscellanea

Venue design notes abridged from Feature 3 of the WHO standard [1]:

• Because dBA gets louder as you approach the speakers, think about whether the area near the speakers is above the volume limit. In a perfect world everyone would be the same distance from the speakers. This is why it is good to "fly" the speakers above head height, and to distribute speakers throughout the space.
• Reverberant spaces increase the noise level and diminish the music's clarity and detail. Less reverb, i.e. a "drier" space, means more bang for less sound level.
• It's good to have a louder and a quieter part of the floor so that people can choose their level.
• You can both provide free disposable earplugs and sell reusable "high-fidelity" or "concert" earplugs at the door. Custom-molded earplugs are the choice of audio professionals.

Many techniques are available to increase perceived loudness level without actually increasing sound pressure level. In situations where the sound limit is difficult to adhere to, radio-style processing such as a multiband compressor is the first tool you should reach for. [4]

Bibliography